What synthetic sweetener, made from aspartic acid and phenylalanine, is commonly used in diet soft drinks?

The synthetic sweetener commonly used in diet soft drinks, which is crafted from the amino acids aspartic acid and phenylalanine, is aspartame. This compound is much sweeter than sucrose, allowing it to provide the desired sweetness at much lower concentrations. Aspartame is notable for having a caloric content that is low enough to be classified as a non-caloric sweetener in practical terms when used in food formulations, making it a popular choice for low-calorie and sugar-free products.

The other options do not align with this description: sorbitol is a sugar alcohol used as a sweetener but has a significantly different chemical structure and is less sweet than aspartame; saccharin is another artificial sweetener but is not derived from the same amino acids; and cyclamates are also synthetic sweeteners but have a different chemical makeup and are not typically used in many markets today due to regulatory issues. Thus, aspartame stands out as the correct answer due to its specific composition and common use in diet beverages.